The invention relates to a vibration damper for towed bodies and more particularly to a damping section of a towed body also serving as hitching means. More particularily, this section forms the head section of a linear underwater antenna towed by a boat, called a "streamer".
These streamers are generally intended to contain detection and measuring instruments and must be protected from the vibrations of the towing boat as well as from the wash created in its wake.
It is a question then of mechanically decoupling a towed body from the towing cable (or other devices) so as to prevent any vibration from the boat being transmitted to the towed instrument carrying body. These vibrations may have several origins such as the movement of the towing vehicle or the turbulence of the limit layer along the cable.
In the case where the towed body is a streamer, specific requirements appear, namely:
sealing and immersibility,
independence at the static pressure,
controllable density,
winding under a tractive force,
severe environment (sea, ozone, UV light, . . . )
passage of connecting cables for connecting
the instruments contained in the streamer to the towing boat.
It is known to insert between the towed body and the towing vehicle a section made from a controlled loss material. This material has a loss angle whose value is such that correct damping of the vibrations is obtained.
It will be recalled that a loss material is a material which, undergoing a stress tending to deform it, shows a certain delay in deformation with respect to the time of application of the stress. Whereby, after removal of the stress, it resumes its original shape after a certain delay.
The loss angle of a loss material characterizes this delay existing between the application or removal of the stress and the deformation of the material.
Since the material, by definition, is not perfectly elastic, such a damper is subjected to the severe conditions of use and storage, such as is the case for streamers, and does not have a long lifespan.
It is also known to use mass-spring type devices or else dashpot type devices (piston-diaphragm). However these devices are not suitable because of the requirement of winding under a tractive force.
The invention arranges then for using a loss material. More particularly, the vibration damper of the invention will be designed so that the tractive forces give rise to losses in a "loss" material so that this material works under good conditions. The loss material used may just as well be, in the embodiment of the invention, a solid material as a viscous liquid material.